This invention relates to smoke detectors operating on the reflected light principle, in which a dark chamber is provided with means allowing ambient atmosphere to diffuse into the chamber, with a light source projecting a light beam across the chamber. A photo-cell is positioned to view the center of the light beam transversely. When smoke enters the chamber, light reflected from smoke particles onto the photo-cell causes the resistance of the photo-cell to decrease. The decrease in resistance corresponding to a predetermined smoke concentration is utilized to actuate an alarm through suitable circuitry.
In the construction of such a device, the accurate positioning of the light source, photo-cell, and the components forming the dark chamber is essential, to provide consistency in calibration and sensitivity. In volume production, the assembly must be accomplished both accurately and economically.
In U.S. Pat. No. 3,799,670 there is illustrated a smoke detector of the above-described type, which utilizes a housing formed of injection molded components formed to facilitate accurate assembly. Although the specific embodiment of the detector illustrated in said patent has achieved considerable commercial success, the number of mechanical components of the detector results in an assembly cost that is higher than desired. Also, the greater the number of components, the greater the chance for errors in assembly.